The subject matter of this disclosure relates generally power conversion systems and their use. In particular the subject matter of this invention relates to power converters, and to systems and methods for connecting high frequency-high voltage, transformer series connected converters between a power grid and a load.
Multilevel inverters have now become proven technology in medium and high voltage applications. They have the advantage of producing high voltage, high power capability with improved voltage quality. Multilevel inverters also eliminate the use of problematic series-parallel connections of switching devices.
Recent advances in power semiconductor technology results in development of fast switching devices such as IGBTs and MOSFETs. Such technology has enabled the use of high frequency switching modulation techniques in power inverters to reduce the harmonic content in output voltages. Switching frequency is increased to reduce the filtering requirement in almost all inverter topologies. The increased switching frequency, however, disadvantageously increases the switching losses, thus reducing the system efficiency. Since there are twelve switching devices in a three-level inverter, switching loss problems have become ever more significant. Inverters therefore suffer greater losses with increases in the number of inverter levels.
In view of the foregoing, there is a need for additional improvements in power conversion systems, especially those comprising high frequency-high voltage inverter/converters and which systems and methods reduce losses associated with high pulse wave modulation inverter frequencies.